Luminaires including semiconductor light sources represented by a blue light emitting diode (LED) are spreading. Above all, a white light source that radiates combined light of blue light of the blue LED and light radiated from a phosphor excited by the blue light can be used for a wide range of uses because the white light source can be easily reduced in size and a circuit configuration can be simplified. For example, there is a white light source obtained by combining the blue LED and a YAG phosphor (yttrium aluminum garnet phosphor) excited by the blue light to radiate yellow light. Further, there is a white light source of a high color rendering type added with a red phosphor such as a CASN phosphor in order to improve color rendering properties.
However, the red phosphor represented by the CASN phosphor has a wide radiation spectrum. The radiation spectrum extends to a range exceeding light wavelength of 600 nanometers (nm). On the other hand, the human visibility has a peak near light wavelength of 555 nm and decreases as wavelength is larger. Therefore, if the red phosphor is added in order to improve the color rendering properties, light in a red region with low visibility increases and light emission efficiency falls.